The present invention relates to a system for the surveillance of traffic, more particularly road traffic.
The considerable increase in car parks, which it is impossible to follow up with an appropriate increase in access routes, means that traffic density in the streets of towns, and on main roads and even freeways, increases to enormous proportions at certain hours of the day or on certain days.
It is useful for the authorities whose job it is to ensure a satisfactory flow of motor traffic to receive information on traffic conditions, so that it is possible for them to put into operation diversions onto routes which are less heavily used than those normally taken by motorists.
It is therefore important that information be available at all times for a certain section of main road or by-road concerning the number of vehicles in that section, their speed, the distance between them, and their size, this information enabling the state of traffic on the section in question to be known.
This information, or certain aspects of it, is conventionally obtained by means of known devices.
It is known to use counters which, at the point at which they are installed, record the passage of vehicles and thus give an indication of the number of vehicles passing this point.
Television cameras have also been set up on highway sections to be kept under surveillance which enable the situation to be seen on an associated receiver.
In this case, however, insufficient information is obtained regarding the distance between vehicles, their speed, etc.
Radars, generally Doppler radars, have also been set up which enable information to be obtained at the point at which they are positioned concerning the speed of vehicles which enter their operating area, the distance separating them and their position.
Nevertheless, under the conditions in which they were used and considering the way in which they were installed, it proved difficult, if not impossible, to cover a relatively long section of road with radars and to extract useful information from them.
The present invention is intended to overcome the drawbacks which have been pointed out and in particular those encountered with radars.
According to the invention, there is provided a system for the surveillance of traffic within a zone which covers a certain length of a route traversed by vehicles concerning which it is desired to gather information, this information relating, inter alia, to their number, size, position, speed and relative spacing. This information is supplied by radar equipment operating in the surveyed area, this equipment being connected to a transmitter/receiver antenna formed by a transmission line which is subject to leakage along its whole length, the line extending substantially over the full length of the zone to be covered.
A system of this type clearly avoids the disadvantages pointed out for prior-art systems, and enables all sorts of information of a radar nature to be obtained for any vehicle situated in the effective area of the radar employed, this effective area being determined by the way in which the leak line, which is used as an antenna, is installed and by its length.